Charles e



(No Model.)

0. E. SGRIBNER.

TEST CIRCUIT FOR MULTIPLE SWITCH BOARDS.

No. 483,047. Patented July 29, 1890.

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UNITED STATES PATENT OFFICE.

CHARLES E. SCRIBNER, OF CHICAGO, ILLINOIS, ASSIGNOR TO THE \VESTERN ELECTRIC COMPANY, OF SAME PLACE.

TEST-Cl RCU IT FO R M U LTI PLE SWITCH-BOARDS.

SPECIFICATION forming part of Letters Patent No. 433,047, dated July 29, 1890.

Application filed June 6,1888- Serial No. 276,210. (No model.)

To alt whom it may concern: jack switches b (Z upon the diiferent boards Be 1t known that I, CHARLES E. SCRIBNER, and to ground. In like manner telepl1011e a citizen of the United States, residing at Chiline 6 extends through switches f g h on the cago, 111 the county of Cook and State of Illidifferent boards and from contact of the 5 nois, have invented a certain new and useful switch of the last board to ground. I have Improvement in Test-Circuits for Multiple not deemed it necessary to show the inde- Sw1tch-Boards, (Case 160,) of which thefollowpendent circuits for the signaling between ing 1s a full, clear, concise, and exact descripthe operators at the central oiiice and the subtlon, reference being had to the accompanying scribers, such circuits and the apparatus con- 1c drawing, forming a part of this specification. nected therewith being well known in the art.

My invention relates to testing apparatus The key-board apparatus of the boards 1 for multiple switch-boards, andits objectis to and 3 is of well-known construction and arprovide ready means of determining at one rangement, and therefore needs no detailed switch-board whether a line wanted or called description. 5 x5 for 15 connected or in use at any other of the In connection with board 2, I have shown boards. a testing apparatus. Such a testing appa- In my patent, No. 885,205, granted June 26, ratus, it will be understood, is used at each I888, I have shown a testing system which is of the boards. The electro-maguetis provided 1n some respects similar to the system herein with two windings, the winding 2' being of 20 described. In said patent I have shown an coarse wire of, say, one-half an ohm resistance, apparatus for testing lines in both directions, and the winding It being of fine wire, say, of the circuits being so arranged that the resistfifty ohms resistance. The battery Z may conance of the clearing out annunciators under sist of three or four cells included in a circuit certain conditions will be removed from the, of said electro-magnet. The armature-lever 2 5 circuit when the test is made. m of the electro-magnet is included in a shunt Myinvention herein relates more especially around the fine-wire winding 7.1. The windto the system of telephone exchange in which ing i is of such low resistance that the curthe signals between the subscribers and the rent from battery I, when sent to line or operators at the central ofiice are transmitted through any considerable resistance, will not 3 over independent wires, one of these indebe suificient to magnetize the electro-magnet pendent wires being common to several subsufiiciently to move the armature m away scribers stations. This system is known genfrom its back contact-point, so as to open the erally as the Firman system or the Law shunt around the high resistance It. If, howsystem. In the Firinan system no individual ever, current is sent from battery I through 35 annunciators are required in the telephonethe low-resistance winding directly to ground lines and no clearing-out annunciators are re theelectro-inagnet willbe of sufiicient strength quired in the connectingcords. My inven to attract its armature and move the armation, therefore, as claimed in my said appliture-lever m away from its back contact, so cation filedDeceinber 27, 1886, is not adapted as to open the shunt around the high-resist- 9o 40 for use in telephone-exchanges in which the ance winding 7:. hen the shunt is thus connection between subscribers and operaopened, and the two windings 'L' k are brought tors is carried on over independent circuits. into circuit, battery Z will be sufficient to mag- My invention herein will be readily undernetize the electro-magnet sufiiciently to cause stood by reference to the accompanying drawit to retain its armature, though the circuit 45 ing,in whichIhave shown two telephone-lines may be closed through considerable resistconnected Withswitches on eachof three multianceas, for example, the resistance of the ple switch-boards and directly to the ground, line from the central ofiice to the subscribers the connecting apparatus being shown at two station. I preferably includea buzzer n in of the boards and the testing apparatus at a local circuit with the armature-lever m in 1o: 5 one board only. such manner that when the armature is Telephone-line a extends through springdrawn to the poles of the electro-magnct this 7 line, as shown; and listening to the buzzer n.

If theline a is closed directly to ground from switch d, as shown, it is evident that as the tip of the plug 0 first touches the spring of switch c,and before said switch is lifted from its contact, current from battery Z will be sent through low-resistance winding "i directly to ground through switch d, thus opening the shunt around winding is; plug 0 being inserted further lifts the spring of switch 0, thus opening the ground portion of line a at the central office, as shown. Batterylwill then be closed through winding?) and also through high resistance and thence through the line a to subscribers station upon line a. This resistance of line a, will not be so high but that the current from battery Z will be suflicient to magnetize the electro-magnet and thus retain the armature m in the position shown, so that the buzzer will respond. The vibration of buzzer n will indicate that the line is free. Suppose, however, that line a is connected with another line at switch d, the circuit then which would be closed when the tip of plug 0 should touch the spring of switch 0 would be of so high resistance that batteryl closed through low-resistance winding 1 and the resistance of the connected line, would not be sufficient to magnetize the electro-magnet so as to move the armature m. Thus the bell or-buzzer a would not respond. On inserting the plug 0 further into the switch 0, the direct ground is opened and we have included in the circuit of battery Z the resistance of the line a from switch 0 to the subscribers station. This resistance of the circuit of battery Z, through low-resistance winding 1' would be so great that the electro-magnet would not draw the armature m to its poles. Thus if the line tested were in use at switch d or any other switch between switch 0 and ground, buzzer 01 would not respond. Suppose, however, a connection were made with line aat switch I; of board 1, the line a would be open at switch I) but closed directly to ground, as shown, through switch (:1. Under these conditions the tip of plug 0 as it was thrust into switch 0 would for an instant close the circuit of battery Z directly to ground. This closing of the circuit is however immediately followed by a complete break when the spring of switch 0 is lifted from its contact by the insertion of the plug. The interval between the closing of the circuit and the break would be so short that the bell n would not vibrate. One observing the armature m at this time would see a slight motion. It

would start toward its front contact, but would immediately fly back without having closed the circuit of the vibrating bell or buzzer n. It will thus be seen that by my apparatus the line is tested in two directions: first, toward the ground at the central station, and next, over the line to the subscribers station. If the line is not connected at a switch toward the office ground no direct ground connection will be found, and therefore the armature 111 will not move. If, however, a connection with the line has been made at a switch in the opposite direction, as at switch 1), the direct ground circuit which is closed will remain closed for so short an interval of time that the circuit will not be closed through the buzzer n. V

The testing apparatus shown at board 2, while described as a part of the multiple switch-board system and especially designed for testing, is in itself a complete mechanism, and may be used for any purpose for which it may be adapted. The switching device forming a part of this,testing apparatus consists of the flexible cord 19 and the plug 0. It is evident that other connecting devicesmight be used in place of the flexible cord and plug.

The principal feature of this testing apparatus is the electro-magnet provided with two coils, one coil having but a small number of convolutions, and the other, speaking relatively, a large number of convolutions, the coil of the larger number of convolutions being normally shunted or short-circuited by the armature-lever of the electro-magnet when the battery-circuit through the electromagnet isiopen. For convenience,abuzzern and a battery are included in a local-circuit with the armature when the armature is closed upon its front contact or stop. This buzzer may, however, be dispensed with, as the user might, by looking directly at the armature-lever 'm or by noting the sound when the lever is closed against its front stop, determine the condition of the circuit tested.

Having thus described my invention, I claim as new and desire to secure by Letters Pat; ent-- 1. A testing apparatus consisting of a batteryZ and an electromagnet provided with two windings, one of a small number of convolutions and the other of a large number of convolutions included in a ground circuit, a shunt around the high-resistance coil, including the armature-lever and the flexible cord and terminal plug of said circuit, substantially as and for the purpose specified.

2. The combination, with multiple switchboards and telephone-lines connected each with a different switch on each of the boards and from the switch on the last board directly to ground, of testing apparatus at each of the switch-boards, said testing apparatus consisting of a normally-open ground circuitterminating in a movable connecting device, a battery included in said circuit with two coils of an electro-magnet, one of said coils having a small number of conyolutions and the other a large number of convolutions, and the armature-lever of said electro-magnet included in a shunt normally closed around the coil having the greater number of convolutions, whereby it may be determined at any board Whether a line wanted or called for isvconnected or in use at any other of the boards.

3. The combination, With multiple switchboards and telephone-lines connected each with a diiferent switch on each of the boards and from the switch on the last board directly to ground, of testing apparatus consisting of a normally open ground circuit including a battery and two windings of an electro-magnct, said windings being the one of low resistance-say one-half an ohm-and the other winding of high resistance-say fifty ohmsthe armature of said electro-magnet in a shunt which normally short-circuits the high-resistance winding, a local circuit including a battery and bell 0r buzzer n, including the armature-lever and the front stop of said lever, whereby a test may be made at any board to determine whether a line wanted is in use or connected at any other of the boards.

In witness whereof I hereunto subscribe my name this 23d day of May, A. D. 1888.

CHARLES E. SORIBNER.

Witnesses:

GEORGE P. BARTON, CHAS. C. WooDwoRTn. 

